For industrial pressure-sensitive adhesive (PSA) tape applications it is very common to use double-sided pressure-sensitive adhesive tapes in order to bond two materials to one another. For the very wide variety of applications the requirements are in some cases highly specific, with the consequence that stringent requirements are imposed on the corresponding adhesive tapes. In the automobile segment, for example, the requirements very often include high temperature stability and a high level of resistance to solvents and fuels. These properties are met in a very good form by crosslinked acrylate PSAs.
Furthermore, again in the industrial segment, a very wide variety of substrates may be bonded. In this case it may sometimes be of advantage to use heat-activatable adhesives, which above a certain temperature undergo softening, flow very well onto the substrates, and then cool to give a firm bond.
Double-sided PSA tapes which meet different requirements of this kind are already well established.
U.S. Pat. No. 5,593,759 describes a double-sided PSA tape which is composed of a carrier layer coated with two thin PSAs. The carrier layer is composed of a structural adhesive. On thermal activation, the PSA blends with the structural PSA and also cures it. In this way, very firm bonds between two adherends are possible. Nevertheless, this PSA tape has an elementary disadvantage for many applications, namely the fact that the double-sided PSA tape is already tacky on both sides to begin with. There exist a large number of applications in which it is advantageous if the PSA tape is nontacky, at least on one side, and hence possesses optimum repositionability. In U.S. Pat. No. 5,593,759 this advantage is absent.
U.S. Pat. No. 4,248,748 describes heat-activatable polyacrylate PSAs with additions of resin. The additions of resin raise the glass transition temperature of the polyacrylate PSA and hence the tack at room temperature. The heat-activatable PSAs, however, are used only for single-sided PSA tapes (film bonding, etc.). Accordingly, the requirements concerning the bonding of adherends or the anchoring of heat-activatable PSAs to the film are not high.
U.S. Pat. No. 4,199,646 describes heat-activatable PSA tapes where the heat-activatable PSA has an elasticity modulus of 10 to 300 kg/cm2. The modulus at the activation temperature is therefore at the level of PSAs at room temperature. In this patent as well, in analogy to U.S. Pat. No. 4,248,748, the bond strength and the elasticity are controlled via the composition of the PSA. Furthermore, only double-sided heat-activatable PSA tapes are described, which can be activated by heat only on both sides.
The multiplicity of PSA tapes described illustrates the great demand which exists for such PSA tapes. It is desirable, however, to simplify further the construction of PSA tapes of this kind.
The object on which the invention is based is therefore that of specifying a pressure-sensitive adhesive which has an adhesive side and a nonadhesive side. The intention is also to specify a process for preparing a pressure-sensitive adhesive of this kind and also a use for a pressure-sensitive adhesive of this kind.